1. Field of the Invention:
This invention relates to a method of measuring shift of patterns of a diffused semiconductor wafer after growth of an epitaxial layer thereon, and more particularly to a method of measuring the pattern shift without destroying the semiconductor wafer and in a short period of time.
2. Description of the Related Art:
It is essential to control the shift of a buried diffusion pattern after growth of an epitaxial layer in a bipolar transistor in an IC. For this purpose, the growth conditions (such as reaction temperature and reaction speed) should be always controlled to assure constant pattern shift. However, it is very difficult to strictly control the growth conditions since frequent measurement of the pattern shift is inevitable.
Conventionally, the angular lapping stain method is used for this purpose. This method comprises: (1) slicing chips having a buried layer in parallel to and perpendicular to the orientation flat by using a dicing saw; (2) angular polishing of optional surfaces of the sliced tips (.theta.=11.degree. 32'); (3) etching the polished surfaces (Sirtl, 2 to 3 seconds); and (4) measuring the shift of the patterns of the buried layers by using differential, interference micrographs (x 150).
The pattern shift factor is obtained by the following equation: ##EQU1##
However since it takes approximately two hours to measure the pattern shift and requires destruction of specimens, this conventional method cannot be used so frequently and is rather expensive.
To solve the problem of the conventional method, some proposals are made to perform the pattern shift measurement through non-destructive tests as disclosed in such publications as Japanese Patent Laid Open Publications 64-31413 and 64-31414. Under the present circumstances, there is a great demand for a more simplified and reliable method of measuring the pattern shift.